1. Field of the Invention
This invention relates to organosiloxane compounds containing ionically charged inorganic metal oxide complexes referred to as polyoxometalates. More particularly, this invention relates to organosiloxane compounds containing covalent bonds to the oxygen atoms of polyoxometalate (POM) structures.
2. Background Information
The chemical literature describes a class of ionically charged water-soluble oxides derived from polyvalent metals such as molybdenum, tungsten, and vanadium. Oxides of this type containing only the polyvalent metal and oxygen are referred to in the literature as "isopoly anions" or "isopoly complexes" and can be represented by the formula (M'.sub.m O.sub.y).sup.p. Anionic heteropoly complexes contain an additional metallic or non-metallic element such as hydrogen, phosphorus and silicon, and have been represented by the formula (X.sub.x M.sub.m O.sub.y).sup.q.
In the foregoing formulae M' is a polyvalent metal, M is molybdenum, tungsten, vanadium niobium or tantalum, X represents the "hetero" atom, i.e. the additional non-metallic or metallic element, m, x and y are integers and p and q represent the charge on the complex, which can be calculated by adding the products obtained by multiplying the valences of X, M, and O by the value of the integer m, x or y associated with that atom. The values of p and q are negative except when M' is aluminum or gallium. The published literature reports that X can be any of at least 65 metallic or non-metallic elements.
A thorough discussion of polyoxometalates is contained in a text by M. T. Pope entitled "Heteropoly and Isopoly Oxometalates" published in 1983 by Springer Verlag. When the values of p and q in the foregoing formula are negative the oxometalate anions are associated with cations that are typically hydrogen, alkali metals, alkaline earth metals, NH.sub.4.sup.+ or R.sub.4 N.sup.+, where R represents a monovalent hydrocarbon radical. The type of anion will affect the chemical and physical properties of the polyoxometalate, including solubility, and the properties of reaction products of the POM.
While there are a very large number of known polyoxometalates, investigators have found that most of these can be characterized by relatively few structures. These structures consist of groups of MO.sub.6 octahedra and XO.sub.4 tetrahedra that share edges, corners, and, occasionally, faces with adjacent polyhedra.
The structure of a particular polyoxometalate, the heteropolyacid H.sub.3 PW.sub.12 O.sub.40 .multidot.6H.sub.2 O, was described by J. F. Keggin, Nature, 1933, 131, p. 908 as a cluster of edge-shared polyhedra, and his name has been given to the polyhedron type of POM structure.
The structures of a number of POM's is discussed in the aforementioned text by Pope, in a text by M. Pope and A. Muller in Angew. Chem., ( International English Edition), 30 (1991) 34-48, by G. Tsigdinos in an article entitled "Heteropoly Compounds of Molybdenum and Tungsten" that is part of a collection entitled Topics In Current Chemistry, 1978, 76, P. 1, and by V. Day and W. Klemperer in Science, 1985, 228, P. 553.
Of particular interest are POM's containing vanadium, molybdenum, tungsten, niobium and tantalum in combination with hydrogen, phosphorus or silicon as the heteroatom.
It has been reported that the chemical and physical properties of POM's can be varied over a wide range by choice of the appropriate polyvalent metal and heteroatoms.
Keggin structure anions of the formula (XM.sub.12 O.sub.40).sup.n- where M is molybdenum or tungsten, X is Si.sup.4+, P.sup.5+, B.sup.3+, Ge.sup.4+, Co.sup.2+ or Co.sup.3+ have been defined in the literature. When X is silicon and M is tungsten or molybdenum, n is 4.
Under mildly basic conditions, one or more of the MO groups from a POM anion can be removed to form a deficient or "lacunary" structure. The structure resulting from removal of one MO group can be represented by the formula XM.sub.11 O.sub.39.sup.p-. The vacancy left by the departing group can be filled with other atoms or groups.
Another common structure of polyoxometalates is referred to as a Dawson structure and is represented by the formula X.sub.2 M.sub.18 O.sub.62.sup.p-. The heteroatom represented by X in this structure is phosphorus or arsenic, and the structure conceptually resembles a dimer of a deficient or "lacunary" Keggin structure in which three of the twelve M atoms have been removed. When the oxygen atoms are omitted the transformation to a Dawson type structure can be represented as EQU XM.sub.12 -3M.fwdarw.XM.sub.9 .times.2=X.sub.2 M.sub.18.
Reactions of the lacunary POM W.sub.11 SiO.sub.39.sup.8- with monohydrocarbyltrichlorosilanes, RSiCl.sub.3, have been reported by W. Knoth [J. Am. Chem. Soc., 101: 3, 759-760 (1979) . When the reaction is carried out in an unbuffered aqueous solution, the WO.sup.4+ unit required for a complete or "non-lacunary" structure is replaced with an (RSi).sub.2 O.sup.4+ group in which each of the two silicon atoms is bonded to two oxygen atoms of the POM and the product corresponds to the formula (RSi).sub.2 W.sub.11 SiO.sub.40.sup.4+.
The reaction of monohydrocarbylsilanes RSiX.sub.3 with the potassium and ammonium derivatives of the same lacunary POM used by Knoth is described by P. Judeinstein et al. [J. Chem. Soc., Dalton Trans. (1991) 1991-1997]. In the formula for the silane R is ethyl, vinyl, decyl or phenyl and X is chlorine or alkoxy. In one of the examples, K.sub.4 SiW.sub.11 O.sub.39 and vinyltriethoxysilane are reacted in an aqueous solution and the product isolated as the tetrabutylammonium salt of the formula [Bu.sub.4 N].sub.4 SiW.sub.11 O.sub.39 O(SiCH.dbd.CH.sub.2).sub.2.
The incorporation of POM structures into organic polymers by reacting the vinyltrichlorosilane/POM reaction product described in the immediately preceding paragraph or the corresponding allyl- or 3-methacryloxypropyl trichlorosilane/POM reaction product with styrene or methyl methacrylate using a free radical polymerization is described by P. Judeinstein in Chemistry of Materials, 4, 4-7 (1992).
The reaction of the trivacant lacunary anion SiW.sub.9 O.sub.34.sup.10- with R'SiCl.sub.3 where R' is hydrogen, ethyl, n-butyl, vinyl, phenyl or p-tolyl is reported by N. Ammari [New. J. Chem, 15, 607-608 (1991)].
The present inventors are not aware of any attempts by others to incorporate POM structures into organosiloxane oligomers and polymers. The difference in physical, electrical, and other properties between cured polyorganosiloxanes and POM's should provide unique property combinations if it were possible to incorporate POM structures into polyorganosiloxane molecules.
One objective of this invention is to incorporate polyoxometalate (POM) structures into organosiloxane polymers and oligomers by means of covalent bonding.